But maybe there are good as well as shabby reasons why Corbyn’s past has failed to detach supporters from his cause. Until now the hypocritical, and in my view despicable, strain of thought that Corbyn represents has been dominant in the universities, the arts, political comedy and much, but not all, of the left-wing media. In what passes for liberal culture it is commonplace to condemn Western crimes while ignoring or excusing the crimes of anti-Western regimes and movements. But, politically, what artists and academics think has had little effect. The attitude of a British government that puts arms contracts before human rights in its dealings with, say, Saudi Arabia mattered far more for the glaringly obvious reason that it was in power and the Left was not.

Friends and comrades have ignored those of us who warned for years about the ugly turn much of left-wing thought has taken. Why, they ask, should we waste our political energies on minor Labour and Liberal Democrat MPs who pander to anti-Semitism or writers who cheer on Islamists while hounding Muslim liberals? Real power, the power that mattered and needed opposing, lay elsewhere.

They did not understand that cultural power will eventually become political power, if no one takes the time to challenge it. Millions voted for UKIP because for decades civilised conservatives were too frightened or too lazy to take on the brutish arguments of the right-wing press. The rise of Corbyn represents the equal failure of a generation of moderate centre-left politicians and activists to recognise that ideology matters, and that if you do not take on your opponents’ ideas today, your opponents will take you over tomorrow.

Leftists have not listened for a second reason, which hardly anyone has mentioned. The centrist politicians they ask Labour members to admire can be as implicated with the world’s dictatorships as thoroughly as the far Left, not just for reasons of state when they are in office but as a means of personal enrichment when they leave it.

Do not think that support for Putin is confined to the extremes of politics. Peter Mandelson left government and founded a lobbying company called Global Counsel. Its clients include Putin’s tame oligarchs, most notably Oleg Deripaska. Lord Mandelson himself goes to St Petersburg to add what credibility he possesses to the propagandistic conferences Putin stages.

Jeremy Corbyn has never pocketed thirty pieces of silver. He says what he says because he means it, not because he has been paid to say it. This does not make him morally superior in my eyes. I distrust a convinced fanatic far more than I distrust an averagely compromised man. But my eyes are not the eyes of most Labour members. Mandelson has moved into a world they deplore. So has David Blunkett, who has joined the board of Oracle Capital, a group “dedicated to providing personalised services to high-net-worth individuals and their families,” with particular emphasis on offering advice to Russian and Chinese multimillionaires. So have dozens upon dozens of New Labour politicians and apparatchiks. So has, of course, Blair himself.